Actually i had a better version of this:

Person A: says "hello Joe" Person B: answers: "Great to see you again buddy!"

After posting message, sender hashes his message with secret salt: "hello Joe" -> 2959D03A72B897C and then posts secret, real text to https://secret-share/#2959D03A72B897C

Receiver does the same to read the actual message.

Fun part?

Sender and receiver can actually piggyback on other people's conversations, twitter feeds, newpaper headlines this way to hide secret messages.